mystic-crypt is designed as a Java library that can be used for simple and complex encryption and decryption.
The source code for the library is available under https://github.com/astrapi69/mystic-crypt
For demonstration what the library can do there is a graphical client:
The source code for the ui is available under https://github.com/astrapi69/mystic-crypt-ui
...Built specifically for Linux and AIX. Now supports key change auditing and key descriptors (uKAD). Check the Project News under the Develop section for more information.
Project source code has moved to https://github.com/scsitape/stenc